1. Field of the Invention
The present invention relates in general to a steering assist apparatus which operates when a vehicle moves back for parking, and more particularly to an apparatus for superimposing to display the display information used to assist the steering wheel handling during parking on a monitor screen in which the rear side of a vehicle is image-picked up.
2. Description of the Related Art
Heretofore, there has been proposed an apparatus in which in the case where a vehicle is moving back and a driver can not see the target place since this place is in a blind spot, the rear field of view of the vehicle is displayed on a monitor. For example, in Japanese Patent Examined Publication No. 2-36417, there is disclosed a monitoring apparatus for displaying thereon the rear side of a vehicle including: a television camera for photographing the rear side of a vehicle; a monitoring television for displaying thereon an image which has been photographed by the television camera; a sensor for outputting an information signal relating to a tire steering angle; and a circuit for generating a marker signal in accordance with the information signal outputted from the sensor to superimpose a marker on a picture of a television for display. In this apparatus, the steering angle data of the tires and the marker position data along the backing direction of a vehicle corresponding to the steering angle are both stored in a ROM, and the expected backing locus of the vehicle corresponding to the steering angle at this time is displayed as a line of a marker on the television screen with the expected backing locus superimposed on the image which has been photographed by the television camera.
In accordance with such an apparatus, when the vehicle moves back, the rear field of view such as of the road situation and the expected backing locus of the vehicle corresponding to the steering angle are both displayed on the screen of the monitoring television. Therefore, a driver can move the vehicle back by manipulating the steering while looking at the television screen without turning back.
However, if such a conventional apparatus is intended to be applied to the parking operation, then the following problems arise. That is, for the conventional expected backing locus, the information relating to the length corresponding to the distance determined between the rear part of a vehicle and the rear of the vehicle, e.g., the length corresponding to the distance of about 2.5 m from the rear part of the vehicle is always displayed on the monitoring television. Therefore, there arises a problem that when the position of the vehicle turns largely from the target parking space, the length of the expected backing locus becomes insufficient since the expected backing locus is also largely curved on the monitor screen, and hence the head part of the expected backing locus is terminated before the target parking space on the monitor screen so that it is difficult to finally judge whether or not, the vehicle can move to the target parking space. On the other hand, if the length of the expected backing locus is made too long in order to solve such a problem, when the amount of turning the vehicle to the target parking space is small, since the expected backing locus is also not curved so much on the monitor screen, the length of the expected backing locus is more than enough. Therefore, there arises a problem that the vicinity of the head part of the expected backing locus goes beyond the target parking space to be projected therefrom, and hence this situation leads to a display which is difficult for a driver to percept.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide a steering assist apparatus in which the expected backing locus has a suitable length corresponding to the position of a vehicle to a target space.
In order to attain the above-mentioned object, according to the present invention, there is provided a steering assist apparatus including: a camera for photographing the rear of a vehicle; a monitor for displaying thereon the image of the rear of the vehicle which has been photographed by the camera; a steering angle sensor for detecting a steering angle of a steering wheel; locus deriving means for deriving a vehicle locus guide line having a fixed basic length and an extension length corresponding to the steering angle; and display control means for superimposing and displaying the vehicle locus guide line and the image on the rear of the vehicle on the monitor.